The invention relates to an optical switch unit having input-ports and output-ports for optical signals. Then, the optical switch unit can selectively switch inner switch elements for connecting an optical input port to an optical port.
In recent years, large scale optical switch units having comparatively many input ports have been proposed. For example, a 32xc3x9732 optical switch unit has 32 input ports and 32 output ports. And, an optical signal inputted in any one of the input ports can be selectively output from any one of the output ports.
These large scale optical switch units are comprised of some smaller scale waveguide-type optical matrix switches, e.g., waveguide-type 8xc3x978 optical matrix switches. In order to increase the number of output ports, these smaller waveguide-type optical matrix switches form multistage-connections.
Regarding these multistage waveguide-type optical matrix switches, a three-stage construction applying to a cross-network is used generally, e.g., xe2x80x9cOptical Switch Architectures for Optical Path Cross-Connectxe2x80x9d; Tetuya Nishi, Satoshi Kuroyanagi and Tomohiro Ishihara; Proceedings of the 1998 IEICE General Conference, B-10-97(March 1998) discloses these constructions.
Though, these present optical switch units constructed by multistage-connecting of the waveguide-type optical matrix switches have a problem that the present optical switch units have comparative large insertion losses because they need three-stage-connecting of the waveguide-type optical matrix switches and each of them has large insertion loss.
Therefore, the present optical switch units additionally need optical amplifiers for compensating the insertion loss.
For example, each of silica-based 8xc3x978 matrix switches has about 5 dB insertion loss, then three-stage-connecting of the 8xc3x978 matrix switches has more than 15 dB insertion loss totally.
Also in Clos-networks, the present optical switch units need three-stage constructions, and three-stage boards were needed for containing the optical matrix switches. For inter-board connection of the three-stage boards, connections occur at two sections and each of the two sections needs about r2 lines for inter-board connection, where r is a port number of an optical matrix switch.
Consequently, because a large number lines are centralized in limited area of the optical switch unit, a production process of the optical switch unit is more complicated.
Furthermore, in connection with the complicated production process, when expanding the optical switch unit""s scale, each of the three-stages of the optical switch unit needs additional boards.
It is an object of the invention to provide an large scale optical switch unit having a simple construction and low insertion loss.
To resolve the above problems, a Kxc3x97K optical switch unit according to the present invention is comprised of an input port, a 1xc3x97M optical matrix switch connected with the input port, an Nxc3x97N optical matrix switch connected with the 1xc3x97M optical matrix switch, an Mxc3x971 optical matrix switch connected with the Nxc3x97N optical matrix switch, and an output port connected with the Mxc3x971 optical matrix switch, where K=Mxc3x97N, M and N are integers more than 1.